The present invention relates to refrigeration cycles and more particularly to improved absorption cycles for producing refrigeration using high temperature heat as the driving source.
In an ideal reversible Carnot cycle, the efficiency of the cycle is (T.sub.2 -T.sub.1)/T.sub.2, wherein T.sub.2 and T.sub.1 are the high and low absolute temperatures of operation. Thus, for a given low refrigeration temperature T.sub.1, the higher the input temperature level T.sub.2, the greater will be the efficiency of operation. The coefficient of operation (COP) of a refrigeration cycle is the refrigeration work done divided by the heat energy put in. The maximum COP of a cycle operating between temperatures T.sub.2 and T.sub.1 is that of a Carnot cycle wherein all processes in the cycle are either adiabatic or isothermal.
The basic single-effect absorption cycle (referred to herein as an SEA cycle) has been used for decades. In such a cycle a working pair fluid, e.g., ammonia/water is heated to a temperature and pressure sufficient to boil off the ammonia (NH.sub.3) as a vapor. The high-pressure ammonia vapor is next cooled in a condenser to liquify the ammonia, and the pressure of the liquid ammonia is then reduced so that it may boil at a low, refrigerating temperature. As the ammonia vaporizes in the evaporator, it absorbs heat from the cooling load. The ammonia vapor then goes to an absorber where it is absorbed back into low pressure water coming from the boiler, with the heat of absorption being rejected to a heat sink. The absorbed NH.sub.3 /water solution is then pumped back to the boiler to complete the cycle.
The basic SEA cycle has an undesirable characteristic in that it has an almost constant COP with increasing input temperature. Thus, even though a higher input temperature would normally be thought to provide higher performance from a more efficient cycle, such has not been the case.
A single-effect regenerative absorption refrigeration cycle (herein referred to as 1R cycle) has been proposed (Kim Dao, "A New Absorption Cycle: The Single-Effect Regenerative Absorption Cycle," Lawrence Berkeley Laboratory Report LBL-6879, February, 1978) to overcome the low performance of the basic SEA cycle. The 1R cycle operates with a multistage boiler and a multistage absorber in such a way that each stage of the heat input and heat rejection processes of the cycle occurs essentially at constant temperature rather than at constant pressure. The invention provides improvements in this 1R cycle, as well as in the combined cycles as will be shown in the preferred embodiment disclosed below. The greatest part of the high pressure refrigerant subsequently condensed is generated in an adiabatic multi-section regenerator wherein the greatest part of the heat necessary to generate the high pressure refrigerant comes from the absorption of the vapor from the evaporation into the very weak liquid solution leaving the boiler, this latter process taking place in the regenerator. The more nearly isothermal operation of the multistage boiler and the multistage absorber, and the more nearly adiabatic operation of the regenerator provides a greater COP of the cycle. However, for a desired refrigeration temperature, the previously proposed 1R cycle is limited by having a maximum input temperature which is relatively low.